There's the effect on reddit, I don't feel qualified to quantify it, but it's the smaller of the two.
There's the effect on every single competitor, it's a huge positive one.
Competitors can only grow so fast, infrastructure takes time to scale, communities take time to organize and build. The most similar reddit alternatives (kbin, lemmy, specialized forums) have been growing as quickly as they possible could under the circumstances.
There still not big enough to absorb all of reddit, but they are a lot closer than they were, because of the protest. That's a huge accomplishment, and a long term existential threat to reddit.
To say the "protest has accomplished absolutely nothing" is highly ignorant.